Among the various conventional image forming apparatuses in the art, there are electro-photographic type image forming apparatuses provided with a fixing device for fixing a toner image on a sheet. The image forming apparatus includes a housing, a heat member, and a pressure member in pressure contact with the sheet in cooperation with the heat member. The image forming apparatus is provided with a front cover to cover a front opening of the housing. A nip pressure between the heat member and the pressure member can be changed in interlocking relation to opening/closing motion of the front cover. More specifically the nip pressure at opening state of the front cover is set smaller than the nip pressure at closing state of the front cover for facilitating sheet removal when sheet jamming occurs.